Known in the art is a spark ignition type internal combustion engine provided with a variable compression ratio mechanism able to change a mechanical compression ratio and a variable valve timing mechanism able to control a closing timing of an intake valve, and increasing the mechanical compression ratio and delaying the closing timing of the intake valve as the engine load becomes lower at the time of engine medium and high load operation in the state holding the actual combustion ratio constant (for example, see Japanese Patent Publication (A) No. 2004-218522).
However, in such a variable compression type internal combustion engine, increasing the mechanical compression ratio will increase the combustion pressure, causing intense vibration and noise. In this case, when the vibration and noise from sources other than the engine are high such as when driving, these will drown out the vibration and noise coming from the engine, so there is no problem in particular, but when the vibration and noise coming from sources other than the engine are low such as during idling operation, the vibration and noise coming from the engine will stand out and become a problem. However, in the above internal combustion engine, such a problem is not considered in any way.